Lightsail Data Transfer Overage Charge

To clarify how Amazon Lightsail calculates data transfer pools and why overages occur despite continuous instance runtime:

• Hourly Evaluation: Data transfer allowances are aggregated and evaluated on an hourly basis based on the specific instances active during each hour. It is not a flat monthly calculation applied retroactively at the end of the cycle.

• Instance Deletion & Replacement: When an instance is deleted, its accumulated data transfer usage remains permanently locked into your billing cycle. However, its contribution to the allowance pool stops immediately. A replacement instance only contributes a prorated allowance from its creation timestamp forward.

• Overage Lock-in: If your cumulative data transfer usage exceeded the active pool capacity during earlier hours (e.g., before all 12 instances were active or during replacement windows), an overage is incurred. Adding or replacing instances later expands the pool for future consumption but does not retroactively erase previously locked-in overages.

• Compute Hours vs. Allowance: The 6,532 usage hours represent your cumulative compute runtime used to bill the instance bundles. This metric does not act as a retroactive multiplier to scale your data transfer allowance.

I would do the following: Because Lightsail abstracts granular per-instance data transfer metrics, standard billing reports only show aggregated overages. Since you already have an open Billing Support case, asking for an hourly breakdown will likely result in a generic response about proration.

Instead, ask Support to confirm that the overage is due to the prorated allowance of replaced instances. Because the proration mechanism during instance replacement is a known source of confusion, you can politely request a one-time courtesy waiver for the overage charges, which AWS Support occasionally grants for first-time Lightsail billing misunderstandings.

Based on how Lightsail data transfer allowances work, here's what's happening with your setup:

How Pooled Allowances Work: Data transfer allowances are aggregated for instances of the same bundle type in the same region. With 12 instances of the 1 GB plan in Frankfurt, each providing 2 TB of monthly allowance, your total pooled allowance would be 24 TB (12 × 2 TB) if all instances ran for the entire billing cycle.

Proration and Timing: However, there's an important detail: creating a new instance does not offset existing data transfer overage, and deleting and recreating instances does not reset the data transfer allowance. The allowance is tied to when instances are active during the billing period.

While the documentation doesn't explicitly detail hourly proration calculations, the principle is that your allowance accumulates based on how long each instance has been running during the billing cycle. If some instances were created partway through the month, they would only contribute their proportional share of the 2 TB allowance based on their active time.

Your Specific Situation: With 13.1 TB of outbound transfer and approximately 2.2 TB of overage, this suggests your pooled allowance is around 10.9 TB. This indicates that your instances, having been created at different times during the billing cycle, haven't accumulated the full 24 TB allowance yet.

Monitoring: Unfortunately, Lightsail doesn't provide a detailed breakdown showing individual instance transfer allowances and usage in real-time. The billing information shows aggregate data transfer and overage charges.

Your billing support case is the right path to get a detailed explanation of how your specific allowance was calculated based on your instances' creation dates.
Sources
Amazon Lightsail Pricing
Data transfer in Lightsail - Amazon Lightsail

I have one additional question regarding the calculation.

My billing page currently shows approximately 6,532 instance usage hours for the 1 GB Lightsail bundle.

Could you please explain exactly how this number was calculated?

During this billing cycle, I always had 12 active 1 GB Lightsail instances. If I deleted an instance for any reason, I immediately replaced it with another 1 GB instance in the same Frankfurt region.

Does the 6,532-hour figure represent the total active instance hours that AWS used to calculate my pooled data transfer allowance?

If so, could you please provide the calculation or a breakdown showing how this total was derived?

Thank you.

Could you please let me know how long it usually takes to receive a response from the Billing Support team?

I have been waiting for more than 60 hours, and my support case is still marked as Unassigned.

Thank you!